O-desmethylvenlafaxine is a major metabolite of venlafaxine. Methods to make O-desmethylvenlafaxine are described in U.S. Pat. No. 4,535,186. This method uses benzyl blocking groups leading to relatively low throughput.
A process of making O-desmethylvenlafaxine is also described in WO 00/59851 in which venlafaxine is allowed to react with diphenyl phosphide in THF (generated by adding n-butyl lithium in THF to diphenylphosphine in THF below 0° C.) at reflux for an overnight period. The yield was reported to be 73.8%. Furthermore, the method involved extraction steps involving large volumes of solvent.
The present invention provides a process of making O-desmethylvenlafaxine which is both time and material efficient.